The primary goal of this research is to measure the auditory system's frequency selectivity in binaural listening as exemplified by the critical band. Critical bandwidth will be determined in several dichotic listening tasks, including lateralization and localization under masking, 2-tone masking, and interaural frequency discrimination. Lateralization will also be measured in listeners with a sensorineural hearing impairment. Supplementary measurements are also to be made of loudness adaptation at low levels and of discrimination of changes in the frequency separation between the two components of a 2-tone complex. Lateralization is measured by determining the minimum onset time difference between a tone burst in one ear and a burst of the same frequency in the other ear at which a listener correctly lateralizes the fused image toward the leading ear. The frequency difference between the target burst and an accompanying masking burst is varied parametrically. The critical band is taken as the frequency separation at which the lateralization thershold begins to decrease as the frequency separation is progressively widened. The localization task requires the listener to identify the source of one tone burst coming from one loudspeaker in the presence of another tone burst, of a different frequency, coming from a second loudspeaker. In two-tone masking the detectability of a narrow-band noise is measured in the presence of a pair of tones presented dichotically with a different frequency to each ear. Frequency discrimination is measured by having the listener indicate which ear receives the lower of two frequencies.